In interior and exterior products for vehicles, there has been a high demand for a decorative product including a decorative layer on a first surface (for example, rear surface) of a transparent member so that the decorative layer is visually recognized through the transparent member from a surface (for example, front surface) opposite to the first surface. For example, in a vehicle in which a millimeter radar device is installed, such a decorative product is applied to a radio wave transmission cover used as an emblem portion, which is located in front of the millimeter radar device. Patent document 1 discloses a radio wave transmission cover including a metal film (decorative layer), which is formed by vapor-depositing metal such as indium, and a colored layer such as a black layer on the rear surface of the transparent member, which is formed from a resin material. Such a decorative product obtains a three-dimensional, unique aesthetic appeal as compared to a decorative product including a decorative layer on a front surface of a base.
Further, patent document 2 discloses a technique in which when forming a metal film by performing sputtering on a surface of a base formed from an acrylic resin, the adhesion of the metal film to the base is increased by forming the metal film while performing a plasma treatment in an inert gas atmosphere.